Strange print behaviour in PHP? [duplicate]

问题:

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• Reference — What does this symbol mean in PHP? 18 answers

Why does the following code output 128?

<?php 
    print 4 << 5; 
?>

回答1:

Because it's a bitwise operator. I think it means 4 multiplied to 2^5 because that operator means

Shift the bits of $a $b steps to the left (each step means "multiply by two")

so it's five steps. It's 4 * 2 * 2 * 2 * 2 * 2 (But I'm guessing here; everything happens at bit level).

回答2:

Refer to Bitwise Operators:

We have to find 4 << 5. It means shift the bits of 4 5 times to the left:

4 is 00000000000000000000000000000100
4 << 5 after shifting is 00000000000000000000000010000000
00000000000000000000000010000000 is 2^7 = 2*2*2*2*2*2*2 = 128